Thermostat with stable bimetal support

ABSTRACT

A line-voltage thermostat is described having a snap-switch proportioned to carry heavy line current to an electric room heater. The snap-switch is mounted on a baseplate which is to be mounted on a wall box. The screws used to mount the baseplate have long shanks so as to be accessible well forward of the baseplate. The mounting screws extend through arched straps which are sheared free of the baseplate except at their ends. This avoids upset of the calibration due to deformation of the baseplate during tightening of the mounting screws, considering mainly the area of the baseplate where the switch is mounted. The thermostat has a bimetal held at a hinge point by a singleunique spring. Fixed ears project toward the bimetal to limit the extent the bimetal can be depressed, protecting the switch from damage and from calibration error due to excessive manual force on the bimetal when the thermostat is being installed or serviced.

United States Patent [72] Inventors Jean R. Fortler South Orange, NJ.; Paul M. Moskowitz, Brooklyn, N.Y. [2]] Appl. No. 83,992 [22] Filed Oct. 26, 1970 [45] Patented Dec. 21,1971 [73] Assignee Federal Pacific Electric Company Newark, NJ.

[54] THERMOSTAT WITH STAllLE BIMETAL SUPPORT 4 Claims, 7 Drawing Figs. [52] U.S. Cl 337/372, 337/85, 337/1 1 1, 337/112, 337/379, 337/380 [5 l] Int. Cl Holh 37/04 [50] Field of Search 337/36, 85, l l l, H2, 333, 372, 379, 380,102, 338

[56] References Cited UNITED STATES PATENTS 2,882,371 4/1959 Bishofberger 337/372 2,888,537 5/1959 Meats 337/338 3,466,587 9/1969 Rechou et al 337/379 3,555,482 1/1971 Callihan 3,553,624 [[197] Dalzelletal.

Primary Examiner-Bernard A. Gilheany Assistant Examiner-F. E. Bell Attorney-Paul S. Martin ABSTRACT: A line-voltage thermostat is described having a snap-switch proportioned to carry heavy line. current to an electric room heater. The snap-switch is mounted on a baseplate which is to be mounted on a wall box. The screws used to mount the baseplate have long shanks so as to be accessible well forward of the baseplate. The mounting screws extend through arched straps which are sheared free of the baseplate except at their ends. This avoids upset of the calibration due to deformation of the baseplate during tightening of the mounting screws, considering mainly the area of the baseplate where the switch is mounted.

The thermostat has a bimetal held at a hinge point by a single-unique spring. Fixed ears project toward the bimetal to limit the extent the bimetal can be depressed, protecting the switch from damage and from calibration error due to excessive manual force on the bimetal when the thermostat is being installed or serviced.

PATENIEB DECZI ISII.

TIIERMOSTAT WITII STABLE BIMETAL SUPPORT This invention relates to thermostats having a bimetallic sheet as the room temperature sensor, especially to the linevoltage type of thermostat in which relatively heavy current of an electric heater is carried by a snap-acting switch.

Thermostats of this type are sometimes prone to erratic performance, individually and from one to another in many ostensibly duplicate units coming from a production line. Because this class of product is highly competitive, any improvement looking toward meeting the problems underlying erratic performance must involve intrinsically simple structures and only a bare minimum of assembly labor.

An occasional cause of calibration instability has been corrected and assembly labor has been curtailed by means of a novel biasing spring for the room temperature sensing bimetallic sheet. This spring acts against a supporting plate at an apex, the apex is located easily and with consistency in a slot, and the extremities of the spring are hooks that embrace respective lugs forming a hinge for the bimetallic sheet. These extremities of the spring act very close to the hinge or fulcrum formed by the lugs, thus .holding the bimetal against the fulcrum without biasing the bimetal about the fulcrum. Moreover the cooperation of the apex of the spring in its slot insures consistent and stable location of the hooked extremities of the spring in relation to the hinge axis of the bimetallic sheet. This in turn avoids a cause of calibration instability.

There is a further related cause of calibration trouble. The bimetal is exposed to possible inadvertent pressure and impact when the cover is off and the thermostat is being installed. Related to this is the fact that the bimetallic sheet is coupled to the switch through a calibratedthrust coupling. In case of a blow (for example) on the bimetal, the blow is transmitted via this coupling to the switch. Any resulting deformation of the switch affects its operating point and affects the reverse or bias or reaction force that the switch ordinarily applied to the bimetal, in turn affecting the thermostat calibration. In the illustrative thermostat described below, this problem is solved by interposing a mechanical stop in the path of the bimetal, allowing ample motions of the bimetal for normal operation of the switch but blocking excessive motion of the bimetal and thereby protecting the switch from deformation and, accordingly protecting the thermostat calibration from this potential cause of error.

The nature of the invention will be more fully appreciated from the following detailed'description of an illustrative embodiment of the invention shown in the accompanying drawings. In the drawings:

FIG. I is a central vertical cross section perpendicular to the front of an illustrative thermostat embodying the features of the invention;

FIG. 2 is a front view of the thermostat of FIG. I with the cover and other parts in front of the bimetal removed, certain partly removed parts being shown in cross section; and a portion of the bimetal being broken away;

FIG. 3 is a rear view of the thermostat as in FIG. 2, part of the switch being broken away to expose detail of the baseplate;

FIG. 4 is a horizontal cross section of the thermostat of FIGS. 1-3 looking upward from the plane 44 of FIG. 3;

FIG. 5 is an enlarged detail of FIG. 1;

FIG. 6 is a bottom view of the thermostat baseplate; and

FIG. 7 is a perspective view ofa spring in FIGS. 1-3.

Referring now to the drawings, a wall box B is suitably supported in an opening in wall W. The thermostat has a main mounting plate 10 having side flanges 12 and top and bottom flanges I4 which provide stiffening and which space the central area 16 away from wall W. Arched mounting straps l8 and 20 extend integrally from top and bottom flanges 14 and initially are in the plan of flat central area 16. The edges of these straps are cut clean and do not bind or interlock with the adjoining metal. Horizontal and vertical slots 22 and 24 are provided in straps I8 and 20 for screws 26. Each of these screws has a laterally projecting shoulder or flange 28 overlying strap 18 (20), a fiber washer 30 behind the strap that holds the screw captive, and an elongated stem 32 that has a screwdriver slot at its upper end.

A switch 34 is screwed to area 16 at the rear of the main mounting plate so as to be received in box B. Short posts 34a extend integrally from switch 34 at each of the mounting points, providing an air space between area 16 of main mounting plate 10 and switch 34.

Holes or slots 38 in flanges 14 are provided for admitting and discharging convection air currents, for carrying away heat generated in switch 34. These slots do not extend to the extremities of straps l8 and 20 so that those straps are integral with relatively strong portions of flanges 14.

A secondary plate 40 is secured to main mounting plate I0 by four screws 42 in area 16. These screws extend from the rear of plate 10 through spacing sleeves 44 that are of plastic, ceramic or other solid thermal insulation. The space between plates 10 and 40 is a second convection air space for carrying away any heat that was developed originally in the switch and that reached plate 10 in some small degree. Secondary plate 40 has sidewalls 40a along its vertical margins. At the bottom, each sidewall 40a is bent at right angles to form arms 40b; and bimetal-locating lugs 40c extend from these arms 40b. Arms 40b form a hinge or fulcrum across ambient temperature sensing bimetal 46 near its bottom edge. Lugs 40c extend through a pair of holes 46a in the bimetal. A biasing spring 48 (FIG. 7) has a very wide V-shaped central portion 48a that is received at its apex in a slot 40d. Spring 48 has reverse-bent portions or hooks 48b extending about the upper and lower sides of lugs 40c, bearing against the side of bimetal 46 that faces plate 40. Slot 40d is transverse to plate 40 and is aligned with ears 400. Spring 48 is of wire that is nearly as thick as slot 4011 is wide. Because of the fit of spring part 48a is slot 40d, part of spring 48 near its extremity at the left as viewed in FIG. 2 bears against the bottom face of one lug 40c and part of the spring near its right-hand extremity bears against the top face of the other lug 40a. The overall effect of this configuration is to provide dependable pressure of the spring against bimetal 46, a pressure that remains consistent among many thermostats and mechanically stable in each thermostat. The small movement that may be exerted on the bimetal by one end of the spring acting about the pivot represented by the related arm 40b is canceled by a like opposite movement at the other arm 40b.

Remote from the lower hinged end of the bimetal, near the top of the bimetal, there is a cam-follower in the form of a button 50 secured rigidly to the bimetal. A cam 52 is supported on a rotatable shaft 54 for cooperation with cam-follower 50. A reduced end portion 54a of shaft 54 extends through a hole in secondary plate 40. The shoulder formed by the largediameter portion of shaft 54 at the front of plate 40 forms a stable bearing surface against plate 40. Small diameter portion 54a extends through plate 40. Shaft 54a is held in assembly to plate 40 by a special washer 56 that is force-fitted over shaft extension 54a to bear against a further washer 58 at the back of secondary plate 40.

Switch 34 in the form illustrated, is a double-pole switch, having two separate switching parts of the so-called microswitch or overcentering snap-switch variety. The switch is in a normal" stable configuration when its rod 34b is released, and the switch is operated or moved out of its normal" position when rod 34b is pushed deeper into the switch body. For each pole of the switch, a setscrew 60 is provided in bimetal 46 and cooperates with the end of rod 34b remote from switch 34.' This rod extends through oversize holes in plates 10 and 40, and is guided by a bushing 34c of the switch. The switch biases rod 34b outward, so that rod 34b normally biases its setscrew 60 toward the left (FIG. I) and away from the switch. This effect causes button 50 to bear against cam 52. When the bimetal is subjected to a rising ambient temperature, its center portion becomes arched toward the right as viewed in FIG. 1 causing rod 34!: to reverse the condition of switch 34 from normal" to its operated condition. Screw 60 is used to provide for calibration, and cam 52 enables the user to adjust the set point of the thermostat. Cam 52 has an extreme position or portion (not shown) which coacts with cam follower 52 for deflecting bimetal 46 to the right in such a way as to insure operation of both poles of switch 34 out of their normal condition for even the lowest temperature to be experienced by the thermostat. Cam 52 represents a conventional off" operator for both poles of the switch. Various combinations of switches are used in various thermostats, sometimes including a snap switch at one pole and a slow-acting switch operated by cam follower 62 as the other pole. At other times, both poles of the switch are snap switches and are arranged to operate at or nearly at the same set point.

A transparent cover 64 encloses that portion of the thermostat containing bimetal 46. Slots 64a at the top and bottom provides for convection air currents entering the cover and moving along the front and back of bimetal 46. Knob 66 fixed to shaft 54 operates cam 52. An edge portion of knob 66 extends laterally through a slot (not shown) in cover 64 for changing the set point of the thermostat. A cover plate 68 has lateral lugs that are received in retaining slots 69, one such slot being provided in each sidewall 40a near the bottom thereof and another such slot being provided in each sidewall 400 near the top thereof for receiving lateral lugs of plate 68. All slots 69 open upward, so that plate 68 slides down into the slots, when the plate is being mounted. Cam 52 is received in an oversized hole in plate 68.

A so-called anticipator resistor 70 is held against bimetal 46 by a retaining clip 72 that is riveted to the bimetal. Flexible insulated connecting wires 70a from resistor 70 extend through drawn holes 74 and 76 in plates 40 and 10, respectively. The anticipator wires extend to the rear of plate where suitable electrical connections are made, customarily to the load-side terminals of the two poles of switch 34.

In mounting the thermostat, cover 64 is snapped off the ends of plate 40, knob 66 is removed and plate 68 is slid upward and removed. At the top of the thermostat, slotted stem 32 of one screw 26 is easily engaged for operation because it extends well forward of plate 40, through an oversized hole in that plate. Near the bottom of the thermostat, there is an opening 46b, and stem 32 of the lower screw 26 extends to a convenient level close to the plane of the bimetal for easy access and operation. Screws 26 are therefore easily operable from the front of the thermostat, and they drive their respective straps l8 and firmly backward (and against) the stops 78, careless pressure applied to bimetal 46 could drive rods 34b too far into the body of switch 34, possibly causing permanent deformation or other damage to the switch. This might not disable the switch, but the thermostat calibration could be upset.

We claim:

1. A thermostat having a switch, a supporting structure carrying said switch, a room-temperature responsive bimetallic sheet mechanically coupled in operative relation to said switch, and means for supporting, said bimetallic sheet in operative relation to said switch, said supporting means including a pair of laterally spaced pivot portions overlying said bimetallic sheet adjacent an end thereof, and a spring having a medial apex portion and having hooked extremities bearing against said bimetallic sheet immediately adjacent to said pivot portions, said supporting structure having a slot receiving and locating said medial apex portion of the spring.

2. A thermostat in accordance with claim 1, including positive stop means between said supporting structure and said bimetallic sheet disposed for limiting the motion of the bimetallic sheet toward the switch to protect the switch from damage in case of accidental manual pressure against the bimetallic sheet.

3. A thermostat in accordance with claim 1, wherein said overlying pivot portions include respective supporting lugs extending through apertures in the bimetallic sheet, said hooked extremities of the spring bearing against the side of the bimetallic sheet remote from said overlying pivot portions, said slot in said supporting structure cooperating with said medial apex portion of the spring to insure consistent closely adjacent disposition of said hooked extremities of said spring to said lugs, respectively.

4. A thermostat in accordance with claim 3, wherein said hooked extremities of said spring have portions held laterally against said lugs by said cooperation of said slot with said medial apex portion of the spring. 

1. A thermostat having a switch, a supporting structure carrying said switch, a room-temperature responsive bimetallic sheet mechanically coupled in operative relation to said switch, and means for supporting, said bimetallic sheet in operative relation to said switch, said supporting means including a pair of laterally spaced pivot portions overlying said bimetallic sheet adjacent an end thereof, and a spring having a medial apex portion and having hooked extremities bearing against said bimetallic sheet immediately adjacent to said pivot portions, said supporting structure having a slot receiving and locating said medial apex portion of the spring.
 2. A thermostat in accordance with claim 1, including positive stop means between said supporting structure and said bimetallic sheet disposed for limiting the motion of the bimetallic sheet toward the switch to protect the switch from damage in case of accidental manual pressure against the bimetallic sheet.
 3. A thermostat in accordance with claim 1, wherein said overlying pivot portions include respective supporting lugs extending through apertures in the bimetallic sheet, said hooked extremities of the spring bearing against the side of the bimetallic sheet remote from said overlying pivot portions, said slot in said supporting structure cooperating with said medial apex portion of the spring to insure consistent closely adjacent disposition of said hooked extremities of said spring to said lugs, respectively.
 4. A thermostat in accordance with claim 3, wherein said hooked extremities of said spring have portions held laterally against said lugs by said cooperation of said slot with said medial apex portion of the spring. 